1. Field of the Invention
The present invention relates to novel compositions of matter containing EPDM (ethylene-propylene-diene terpolymer) rubber and/or EPR (ethylene-propylene copolymer) rubber, and silicones, and to a variety of useful articles shaped therefrom.
2. Description of the Prior Art
Rubber/silicone compositions have long been known to this art. They were originally developed with a view towards producing a rubber having the good mechanical properties of organic rubbers and, at the same time, the good thermal behavior of the silicones. This combination of properties is necessary, in fact, for an increasing number of applications, among which electrical insulation and automotive uses are exemplary.
The conventionally employed crosslinking agents therefor are sulfur derivatives and/or an organic peroxide.
Representative prior art describing the use of organic peroxides as crosslinking agents includes:
U.S. Pat. No. 3,227,777 describing the combination EPR-vinylated organopolysiloxane oil or resin, crosslinked with peroxide;
U.S. Pat. No. 3,865,897 describing a method of mixing organic rubber and silicone by shearing at an elevated temperature in order to improve the compatibility of both constituents;
U.S. Pat. No. 4,234,702 (corresponding to GB-A-2,019,417) and EP-A-40,468 which suggest, in order to improve compatibility, adding a diorganopolysiloxane oil in which certain organic groups are notably alkyl radicals containing from 4 to 20 carbon atoms, hydroxyalkyl radicals and polyoxyalkylene radicals;
Japanese patent application KOKAI No. 81-116,739, the subject of which is a composition of:
(i) 100 parts of an EPR or EPDM rubber, PA1 (ii) 1 to 150 parts of an organopolysiloxane resin, PA1 (iii) 10 to 150 parts of a silica having a specific surface area greater than 50 m.sup.2 /g, PA1 (iv) 0.5 to 15 parts of 2-mercaptobenzimidazole, PA1 (v) 0.5 to 15 parts of a phenolic antioxidant, and PA1 (vi) 0.1 to 10 parts of an organic peroxide.
These prior art compositions constitute significant advances relative to the use of organic rubbers alone or of the silicones alone, but shortcomings remain, especially in the case of applications for the automotive industry (manufacture of a variety of articles, particularly of gaskets and belts).
Indeed, it has been determined that the known compositions exhibit, in particular, poor behavior on heat aging, resulting in the appearance of crazing and a considerable reduction in the elongation at break.